With the advent of double overhead camshaft engines, a variety of schemes have been used for driving the dual camshafts on each cylinder bank. On four-stroke cycle engines, it is necessary that the camshafts operate at a rotational speed which is one-half the crankshaft speed. As a result, the driven sprockets attached to the camshafts must be twice the diameter of the drive sprocket, when such sprocket runs at crankshaft speed.
U.S. Pat. No. 5,014,655 to Ampferer discloses a camshaft drive arrangement in which driven sprockets attached to the camshafts are twice the diameter of the drive sprocket, which is attached to a jackshaft driven by the engine's crankshaft. The system of the '655 patent suffers from two general problems. First, the driven sprockets occupy the same plane and, as a result, each cylinder head is much wider than a cylinder head equipped according to the present invention. Similarly, although a cylinder head having the system of the '655 patent could be narrowed by achieving a gear reduction with the jackshaft upon which the drive sprocket is mounted, this would of course necessitate that the added parts of the jackshaft be retained.
It is an advantage of the present invention that a single reduction may be used to drive a camshaft at one-half crankshaft speed, while allowing a narrow valve angle sufficient to form a relatively flat, pent roof combustion chamber for the engine. A system according to the present invention allows the camshaft sprockets to occupy different planes so as to overlap when viewed from either end of the crankshaft. As a result, the cylinder head may be of relatively narrow configuration, as compared with conventional engines.